The hole in the ozone layer over Antarctica is closing later, exposing more plants and animals to harmful UVB radiation, according to a recently published study.
Discovered in the late 1970s, the shrinking ozonosphere in the Antarctic region is in a kind of cycle. The ozone hole opens at the beginning of the southern spring (September) and closes again in October. Yet in recent years, scientists have noted that a series of unusual events have allowed the ozone hole to persist beyond November and into December. According to a study published on April 25 in the scientific journal Global Change Biology, the consequences for local flora and fauna are possible but difficult to assess.
The ozone layer protects us from the sun’s harmful rays, including UVBs, which are responsible for the majority of skin cancers. When the hole in the ozone layer over Antarctica forms, ozonospheric protection no longer works. The UV index, which measures the intensity of solar radiation, takes off, reaching a value of 14, equivalent to that found in the tropics.
Until now, the hole in the ozone layer formed in early spring and closed again at the end of the year. During this time, dormant plant and animal species were protected from the sun’s harmful rays by sea ice or snow on the ground. A situation that could well change as the ozone hole closes later: “Early summertime ozone depletion is concerning: high incident UV-B radiation coincident with snowmelt and emergence of vegetation will mean biota is more exposed.”, note the authors in their study. “The start of summer is also peak breeding season for many animals, thus extreme UV-B exposure […] may come at a vulnerable time in their life cycle.”
The persistence of the ozone hole beyond October has been observed for the 2020s and beyond. For the researchers, the reason is a series of unusual events. The bushfires that ravaged Australia between 2019 and 2020 and the Hunga Tonga volcanic eruption of 2022 emitted large quantities of ozone-destroying aerosols, explaining why the ozone hole failed to close in October.
At the same time, the last four years have seen a reduction in sea ice, further exposing local flora and fauna. Less sea ice or snow cover on the ground means fewer opportunities to shelter from UVB rays, but also less reflection of these same rays through the albedo effect.
The consequences for wildlife are still difficult to assess, says the study, which brings together researchers from the University of Wollongong, Australia, the University of Canterbury and Colorado State University. At present, little research has been carried out into the effects of UV on animals and plants. However, UV rays can cause skin and eye damage. While the animals are protected by their fur and plumage, their eyes are exposed, especially those of young penguins and seals, which are usually born in late spring.
Some species, such as Antarctic algae or plants, produce their own sun protection, just like the royal penguin or the macaroni penguin, which produce eye protection against the sun’s rays. These natural protections are normally adapted to UV levels of around 6. But with levels twice as high, these species will have to consume more energy to produce this solar protection, to the detriment of their development.
But another animal could be at risk from this extreme UV exposure: krill. UV rays can penetrate the ocean, particularly in the absence of sea ice, forcing krill to dive deeper into the ocean, with consequences for other species, as krill are at the base of the Antarctic food chain. “Less sea ice means more radiation penetrates the ocean. When this coincides with ozone depletion, more UV and visible radiation will enter the water column.”, says the study. “Increasing levels of UV radiation are known to impact the behavior and survival of primary producers, with cascading effects to organisms higher up in the food chain.”
While the authors welcome the overall reduction in CFCs, due in particular to the 1987 Montreal Protocol, they nevertheless call for a reduction in CO2 emissions into the atmosphere, in particular to limit bush and forest fires so damaging to the ozone layer.
Mirjana Binggeli, Polar Journal AG
More on the subject
